Soiled human hair is shampooed to remove sebum that is naturally secreted by the head as well as soil and other atmospheric contaminants that accumulate on the hair. Sebum, in particular, accumulates on the hair in a relatively short period of time leaving the hair with a greasy, dirty feel and poor manageability. The most effective shampoos for cleansing the hair for removal of the atmospheric contaminants and sebum, are those that contain high lather synthetic anionic detergents, such as the long chain alkyl sulfates and the partially ethoxylated long chain alkyl sulfates. These synthetic anionic detergents are very effective for cleansing the hair but, after rinsing with water, leave the hair with a dried touch, usually called "creak" and result in hair, when wet, that is in an extremely tangled and unmanageable after-shampoo condition.
Thoroughly cleansed hair is extremely difficult to comb, in either the wet or dry state because the individual hair fibers tend to snarl, kink, and interlock with each other. Particularly prior to complete drying of thoroughly cleansed hair, in this after-shampoo stage, the hair is very difficult to comb or brush. Even after complete drying, the thoroughly cleansed hair remains difficult to comb or brush and does not set well. Thoroughly clean, dried hair also has undesirable electrostatic properties in a low humidity atmosphere that causes the hair to "fly away", thereby further reducing the combing or brushing property of the hair. Generally, these above-outlined problems that result from synthetic detergent cleansing of the hair, particularly the high-lather synthetic anionic detergents, have been alleviated either by the after-shampoo treatment of the hair with hair conditioners, for example in the form of a hair rinse, or by including hair conditioners directly within the shampoo composition.
After-shampoo hair conditioning compositions are easily formulated but are inconvenient to use because of the necessity of applying the conditioner to the hair in a separate stage, after shampooing. The preparation of a conditioning shampoo has been more difficult because of inherent incompatibility problems between anionic surfactants and the fatty cationic compounds that are good conditioning agents. Contact between an anionic surfactant and a cationic surfactant or cationic polymer produces a precipitate that forms immediately or causes an interaction between the anionic and cationic compounds that significantly reduces their respective cleaning and conditioning properties. The reduction in cleansing and conditioning effectiveness is observed even in compositions wherein the anionic and cationic compounds do not precipitate from the composition but remain in solution or suspension. This incompatibility between an anionic surfactant and a cationic conditioning compound is well recognized by those skilled in the art. For example, Sagarin in Cosmetics, Interscience Publishers, Inc., New York, p. 538 (1957), states that anionic and cationic compounds cannot be used in combination because they react to form insoluble salts.
A partial solution to this incompatibility problem in the formulation of conditioning shampoos is exemplified by the following patents that disclose compositions that contain surfactants that are not anionic e.g. non-ionics, amphoterics and zwitterionics together with cationic conditioning compounds: U.S. Pat. No. 3,849,348 to Hewitt; U.S. Pat. No. 3,990,991 to Gerstein; and U.S. Pat. No. 3,822,312 to Sato.
Another problem inherent in formulating a conditioning shampoo is an instability problem that results when water-insoluble conditioning agents are also included in the conditioning shampoo composition, such as the non-volatile silicones that are well recognized in the art as providing a degree of softness to the hair.
Silicones in shampoo compositions have been disclosed in a number of different patents: U.S. Pat. No. 2,826,551, Mar. 11, 1958 to Green; U.S. Pat. No. 3,964,500, June 22, 1976 to Drakoff; U.S. Pat. No. 4,364,837, Dec. 21, 1982 to Pader; British Pat. No. 849,433, Sept 28, 1960 to Woolston; U.S. Pat. No. 4,741,855 to Grote, et al.; U.S. Pat. Nos. 4,788,006 and 4,902,499 to Bolich, Jr. et al. and U.S. Pat. No. 4,704,272 to Oh et al.
A particularly difficult problem to solve in silicone-containing conditioning shampoos is that of keeping a dispersed, insoluble, non-volatile silicone material suspended in stable form while retaining the cleansing and conditioning performance of the conditioning shampoo. The stability problem is particularly prevalent in conditioning shampoos like those disclosed herein containing an anionic surfactant and a cationic conditioning material which, as outlined above, by themselves tend to interact and present stability problems. A variety of materials have been proposed for inclusion in silicone-containing conditioning shampoos for purposes of thickening and stabilization such as xanthan gum, long chain acyl derivatives, long chain amide oxides, and long chain alkanolamides as disclosed in U.S. Pat. Nos. 4,788,006; 4,704,272; and 4,741,855.
In accordance with the present invention, it has been found that water-insoluble di-long chain quaternary ammonium compounds, particularly dioctadecyl ammonium salts, e.g. dioctadecyldimethyl ammonium chloride, cooperate unexpectedly with long chain alkyl sulfates and partially ethoxylated long chain alkyl sulfates, particularly ammonium lauryl sulfate and ammonium lauryl ether sulfate, when the molar ratio of long chain alkyl sulfate and/or long chain alkyl ether sulfate to di-long chain quaternary ammonium compound is at least about 85:1. To achieve the full advantage of the present invention, the molar ratio of alkyl sulfate and/or long chain alkyl ether sulfate to di-long chain quaternary ammonium compound should be at least 100:1, particularly about 100:1 to about 150:1, and up to about 1000:1. At this high ratio of strong anionic detergent to cationic quaternary ammonium compound, essentially no precipitation occurs as a result of the electrostatic interaction between the strongly anionic detergents and the cationic quaternary ammonium compound, but such high ratios have not been used because of the negligible conditioning advantage imparted by the small amount of cationic quaternary ammonium compound.
Surprisingly, it has been found, however, that the unusually high ratio of long chain alkyl sulfate and/or long chain alkyl ether sulfate to di-long chain quaternary ammonium compound lowers the infrared stretching frequency of CH.sub.2 groups in the anionic long chain detergent hydrocarbon chains that are freely moving (as in a liquid) as the temperature is increased to about 30.degree. C. or above. This lowering of stretching frequency at higher temperature is quite unusual since higher temperature normally induces more disorder in a molecule causing the CH.sub.2 stretching to shift to a higher frequency at the higher temperatures. Quite surprisingly, this lower frequency CH2 stretching band at higher temperatures, particularly in the range of about 30.degree. C. to about 50.degree. C. reflects the ability of the compositions of the present invention to incorporate or "solubilize", and/or remove from the hair, various hydrocarbon materials such as conditioning agents, e.g. silicones, long chain hydrocarbons, soil, sebum, dirt and the like. This ability to incorporate or "solubilize" and/or remove these and other compounds in unexpected amounts is due to the interaction between the strongly anionic long chain alkyl sulfate detergents and the di-long chain quaternary ammonium compounds at molar ratios of at least 85:1 sulfate and/or ether sulfate to quat that creates more order to the CH.sub.2 --containing long chain alkyl sulfate and/or alkyl ether sulfate molecules for easier incorporation of materials into the composition and/or removal of materials from the hair. This unexpected increased order to the alkyl sulfate and/or alkyl ether sulfate molecules, at higher temperatures permits conditioning agents and contaminant molecules to be removed easily from the hair at normal hair washing temperatures, e.g. about 30.degree. C. to about 50.degree. C., and permits the incorporation of unexpectedly increased amounts of volatile, non-volatile and rigid silicones and other conditioning agents into the aqueous shampoo compositions.
It should be understood that the use of the terms "solubilize" and "solubilization" as used herein in reference to the ability of the compositions of the present invention to form a stable conditioning shampoo composition or to remove a material from the hair, is not limited to the formation of a true solution of the material in water but used in the broader sense of the capability of forming a functional (in the sense of incorporating or removing) mixture of the material with water as either a stable composition (incorporating) or a mixture of the material with water such that the material can be removed from the hair (removing).